1. Field of the Invention
The present invention relates generally to the structure and use of radiofrequency electrosurgical apparatus for the treatment of solid tissue. More particularly, the present invention relates to an electrosurgical system having pairs of electrodes and electrode arrays which are deployed to treat large volumes of tissue, particularly for the treatment of tumors which lie close to the surface of an organ.
The delivery of radiofrequency energy to target regions within solid tissue is known for a variety of purposes. Of particular interest to the present invention, radiofrequency energy may be delivered to diseased regions in target tissue for the purpose of causing tissue necrosis. For example, the liver is a common depository for metastases of many primary cancers, such as cancers of the stomach, bowel, pancreas, kidney, and lung. Electrosurgical probes for deploying multiple electrodes have been designed for the treatment and necrosis of tumors in the liver and other solid tissues. See, for example, the LeVeen(trademark) Needle Electrode available from RadioTherapeutics Corporation which is constructed generally in accord with published PCT application WO 96/29946.
The probes described in WO 96/29946 comprise a number of independent wire electrodes which are extended into tissue from the distal end of a cannula. The wire electrodes may then be energized in a monopolar or bipolar fashion to heat and necrose tissue within a defined volumetric region of target tissue. In order to assure that the target tissue is adequately treated and to limit damage to adjacent healthy tissues, it is desirable that the array formed by the wire electrodes within the tissue be precisely and uniformly defined. In particular, it is desirable that the independent wire electrodes be evenly and symmetrically spaced-apart so that heat is generated uniformly within the desired target tissue volume. Such uniform placement of the wire electrodes is difficult to achieve when the target tissue volume has non-uniform characteristics, such as density, tissue type, structure, and other discontinuities which could deflect the path of a wire as it is advanced through the tissue.
Of particular interest to the present invention, as recognized by the inventor herein, difficulties have arisen in using the multiple electrode arrangements of WO 96/29946 in treating tumors which lay at or near the surface of an organ, such as the liver. As illustrated in FIG. 1, a LeVeen(trademark) Needle Electrode used for treating a tumor T near the surface S of a liver L can result in at least some of the tips of electrodes 12 emerging from the surface. Such exposure of the needle tips outside of the liver is disadvantageous in a number of respects. First, the presence of active electrodes outside of the confinement of the organ being treated subjects other tissue structures of the patient as well as the treating personnel to risk of accidental contact with the electrodes. Moreover, the presence of all or portions of particular electrodes outside of the tissue being treated can interfere with proper heating of the tissue and control of the power supply driving the electrodes. While it would be possible to further penetrate the needle electrode 10 into the liver tissue, such placement can damage excessive amounts of healthy liver. Moreover, the heating characteristics of the liver tissue near the surface will be different from those of liver tissue away from the surface, rendering proper treatment of the tumor tissue near the surface difficult even if the electrodes are not exposed above the surface.
In addition to difficulties in treating lesions near the surface of an organ, electrosurgical probes for performing large volume tissue ablation can have difficulty in treating highly vascularized tissues and/or tissue near a large blood vessel. In both cases, heat being introduced by the electrode can be rapidly carried away by the blood, making the heating and control of temperature in the tissue difficult.
For all of these reasons, it would be desirable to provide improved electrosurgical methods and systems for treating tumors which lie at or near the surface of an organ or tissue mass. It would be further desirable to provide such improved methods and systems which would be capable of improving beat transfer into and/or temperature uniformity of vascularized tissues where the heat can be taken away by blood flow. It would be particularly desirable if such methods and systems could lessen the risk of accidental exposure of the treating electrodes above the tissue surface. It would be further desirable if the methods and systems would enhance uniform treatment of the entire tumor mass, including those portions which lie near the surface of the organ being treated. Still further, it would be desirable if the methods and systems could achieve treatment of irregularly shaped tumors and tumors which extend from an organ surface to relatively deep within the organ. At least some of these objectives will be met by the invention of the present application.
2. Description of the Background Art
WO 96/29946 describes an electrosurgical probe having deployable electrode elements of the type described above. The LeVeen(trademark) Needle Electrode constructed in accordance with the teachings of WO 96/229946 is available from Radio Therapeutics Corporation, assignee of the present application, and is illustrated in brochure RTC 002 published in 1998. Other electrosurgical devices having deployable electrodes are described in German Patent 2124684 (Stadelmayr); U.S. Pat. Nos. 5,472,441 (Edwards et al.); 5,536,267 (Edwards et al.); and 5,728,143 (Gough et al.); and PCT Publications WO 97/06739; WO 97/06740; WO 97/06855; and WO 97/06857. Medical electrodes having pins and other structures are shown in U.S. Pat. Nos. 3,991,770; Re. 32,066; 4,016,886; 4,140,130; 4,186,729; 4,448,198; 4,651,734; and 4,969,468. A skin surface treatment electrode for the removal of blemishes having a circular array of tissue-penetrating pins is described in Rockwell, The Medical and Surgical Uses of Electricity, E. B. Trent and Co., New York, 1903, at page 558. A cluster electrode comprising a plurality of electrodes projecting from a plate for insertion in tissue is described in WO 99/0410.
The present invention provides improved methods, systems, and kits for performing electrosurgical treatment of tumors and other disease conditions within body organs and other tissue masses. The methods, systems, and kits are particularly useful for treating tumors which lie at or near the surface of an organ, such as the liver, kidney, pancreas, stomach, spleen, particularly the liver. In a first aspect, the present invention relies on applying electrical energy, such as radiofrequency or other high frequency energy, to or between an internal tissue site and an external tissue site on the surface of the organ. The energy may be applied in a monopolar fashion where the internal and external sites are maintained at the same polarity and a dispersive or passive electrode disposed on the patient""s skin is maintained at the opposite polarity. The high frequency energy can be applied simultaneously to both the internal and external sites, but will more usually be applied sequentially to one site and then to the other. The energy may also be applied in a bipolar fashion where the internal treatment site is maintained at one polarity and the external treatment site maintained at the opposite polarity. Monopolar treatment is advantageous in permitting formation of two fully formed lesions (necrosed regions) that can be overlapped to treat a desired region, but is disadvantageous since it requires use of a dispersive electrode. Bipolar treatment eliminates the need for a dispersive electrode and, by proper spacing, permits formation of a single, continuous lesion. Such approaches reduce the risk of passing internally deployed electrode(s) out through the surface of the body organ and enhances the uniform electrosurgical treatment of tissue between the internal and exterior treatment sites.
In a second aspect, the present invention provides for applying electrical energy, such as radiofrequency or other high frequency energy, to an internal tissue site while a cover is deployed over the tissue surface adjacent to the target region within the tissue which is being treated. The cover may comprise electrode(s) as described above. Alternatively, the cover may be electrically neutral (unpowered) and/or electrically insulated to protect surrounding tissue and treating personnel, as described above. Such covers should be capable of compressing the tissue in order to inhibit blood flow to and from the target region being treated. By inhibiting blood flow, energy losses can be minimized and temperature uniformity enhanced. The covers may be rigid plates, conformable surfaces, or the like, and will typically be clipped or otherwise removably or positionably attached to a primary treatment probe. In addition to being electrically insulated, the cover will preferably also be thermally insulating to protect adjacent tissue structures from thermal damage and further to inhibit heat losses from the tissue which is being treated. While in some instances the cover may be discontinuous, i.e., perforated or having other openings or apertures, it will usually be desirable to utilize a cover having a continuous surface which can inhibit the loss of steam from the tissue which is being treated. Containment of steam within the region being treated further enhances tissue heating. Preferably, the compressive force between a deployed electrode array on the primary treatment probe and the cover on the tissue surface will be in the range from 0.5 psi to 1.5 psi, preferably 0.8 psi to 1.2 psi.
A method according to the present invention for treating a target region beneath a tissue surface, such as a tumor site closely beneath the surface of an organ, comprises deploying a first array of electrodes in the tissue at or near the target region, preferably being distal to the site. A second electrode is deployed on the tissue surface over the target region, and an electrical current, typically radio or other high frequency current, is then applied to the tissues through the electrodes. The current may be applied in a monopolar fashion, i.e. with the first array of electrodes and the second electrode being simultaneously and/or successively connected to one pole of a power source and a dispersive or passive electrode disposed on the patient""s outer skin attached to the other pole. Alternatively, the first array of electrodes and the second electrode may be powered in a bipolar fashion by attaching them to opposite poles of the power supply.
The first array of electrodes is preferably deployed by positioning a probe so that a portion of the probe lies near the target region in the tissue to be treated. A plurality of at least three array electrodes is then advanced radially outwardly from the probe to define the first electrode array. The probe may be advanced directly into tissue, e.g. using a sharpened distal tip on the probe itself, or may be introduced together with a stylet which is then removed in order to permit introduction of the electrodes through the probe. Conveniently, the probe for deploying the electrode array may be constructed similarly or identically to a LeVeen(trademark) Needle Electrode as described in WO 96/29946. With such LeVeen(trademark) Needle Electrodes, the electrodes advance initially in the forward direction and then evert (i.e. follow an arcuate path from the tip of the probe) outwardly as they are further advanced into the tissue. The electrodes will preferably deploy outwardly to span a radius of from 0.5 cm to 3 cm when the individual electrode elements are fully extended. The array electrodes may be deployed at a depth below the tissue surface in the range from 2 cm to 10 cm, preferably from 3 cm to 5 cm, (based on the position of the probe tip), with all individual electrode elements preferably lying completely within tissue.
The second electrode may comprise a plate or other electrode structure which is engaged directly against the tissue surface. The plate or other structure will usually have an active electrode area in the range from 3 cm2 to 15 cm2, preferably from 5 cm2 to 10 cm2. The second electrode may further comprise a plurality of tissue-penetrating electrode elements which penetrate into the tissue when the second electrode is engaged against the tissue surface. The tissue-penetrating electrode elements will usually be distributed over an area as set forth above for the plate electrode, and will preferably be capable of being penetrated to a depth below the tissue surface in the range from 3 mm to 10 mm, preferably from 4 mm to 6 mm. The tissue-penetrating elements will usually be parallel to each other, more usually being normal or perpendicular to a planar support plate, and are preferably pins having a diameter in the range from 1 mm to 3 mm, preferably from 1.5 mm to 2 mm, and a length sufficient to provide the tissue penetration depths set forth above. Optionally, the second electrode can be attached to the probe after the first electrode array has been advanced and deployed beneath the tissue. By attaching the second electrode to the probe, the entire system can be immobilized while the target region is being treated.
The active electrode area of both the first electrode array and second electrode will be the surface area of the electrode structure which is expected to come into contact with tissue in order to transfer electrical current. The total active electrode area of the first array of electrodes will typically be in the range from 1 cm2 to 5 cm2, preferably from 2 cm2 to 4 cm2. The area for the exemplary LeVeen(trademark) Needle electrode is about 3 cm2. The active electrode area for the second electrode will be in the ranges generally set forth above. In the case of second electrodes having pins projecting from the surface of a plate, the active electrode area may be defined by the pins, the plate surface, or a combination of both. It will be appreciated that portions of the plate and/or the pins may be covered with electrical and thermal insulation to achieve desired tissue treatment patterns. Portions of the first array of electrodes may also be insulated in order to change the electrical transfer characteristics. For monopolar operation, there is generally no requirement that the electrode areas of the first electrode array and the second electrode be the same. In the case of bipolar operation, however, it will generally be desirable that the total electrode areas of both the first array of electrodes and the second electrode be generally the same, usually differing by no more than 20%, preferably differing by no more than 10%.
In an alternative method according to the present invention, control of heat-mediated necrosis of a target region in tissue may be improved by inhibiting blood flow into the target region prior to the heat treatment. Large volume ablation and necrosis of highly vascularized tissue, such as liver tissue, can be difficult because of thermal transport from the region due to local blood flow. That is, blood flow through the tissue carries heat away. Moreover, because the degree of vascularization in any particular region is unpredictable, the total amount of heat which must be delivered in order to effectively necrose the tissue is difficult to predict. Heat-mediated tissue necrosis may thus be improved by inhibiting blood flow into the treatment region prior to heating. In some instances, it may be possible to tie off or clamp blood vessels(s) going into the region. Other known techniques for inhibiting blood flow and consequent heat loss include lowering blood pressure to reduce blood flow in all regions of the body. For thermal treatment according to the present invention, however, it will be preferred to first necrose tissue at or near a distal periphery of the target region so that the vasculature is at least partly destroyed in order to reduce the blood flow into the and/or the target region. Most preferably, this two-step method will be achieved using the first array of electrodes and second electrode as generally described above, where the second electrode is first energized to necrose tissue at or near the periphery of the target region. While this approach is presently preferred, it will be appreciated that other heating modalities could also be employed, such as microwave heating, dispersed laser energy heating, electrical resistance heating, introduction of heated fluids, and the like.
In a still separate aspect of the methods of the present invention, deployment of the first electrode array and second electrode or other cover in a manner such that tissue is compressed therebetween will (after deployment) also inhibit blood flow into and from the target region between the electrodes. Thus, the step of inhibiting blood flow may be achieved as simply as compressing the tissue in order to reduce blood flow through the target region between the electrodes. The compressive forces may be applied by any structure deployed over or otherwise adjacent to the tissue region being treated, usually being positioned directly over the target region in the organ being treated. Typically, the primary electrode which is deployed within the tissue will act as an anchor and the cover or other structure will be secured to a probe or shaft which is part of the electrode. The cover and electrode can then be drawn together and secured in place to compress all or a portion of the tissue volume being treated. In this way, blood flow into and out of the region may be significantly decreased. Optionally, such compression is achieved using treatment electrodes which are also used for introducing a frequency or other electrical current into the treatment region to effect the heating.
The presence of a cover or second electrode structure can also be relied on to facilitate deployment of the first electrode array. As discussed above, the first electrode array is preferably deployed by positioning a probe so that a portion of the probe lies near the target region in the tissue to be treated. The cover or second electrode structure may be utilized to help initially initial the probe. After determining a desired treatment depth, e.g., based on computed tomography (CT), the position of the cover or second electrode structure on the probe may be fixed so that the distal end of the probe will penetrate tissue to the desired depth when the cover or second electrode structure engages the upper skin or tissue surface. Thus, the cover or second electrode structure may be used as a positioning xe2x80x9cstopxe2x80x9d in the initial deployment of the probe and first electrode array. After deployment of the first electrode array, the cover or second electrode array can optionally be moved toward the first array and the tissue compressed between the two as also described above.
While the preferred compression apparatus will use an anchor electrode and an external compression structure (either electrically active or neutral), it will also be possible to use a pair of spaced-apart structures penetrated into tissue for compressing the tissue therebetween. Either or both of the spaced-apart structures may be electrically active, e.g., acting as energy-applying electrodes for performing the methods of the present invention. Alternatively, the spaced-apart structures may both be electrically unpowered so that they compress tissue only and other electrode(s) are used for directing electrical energy to tissue.
Systems according to the present invention for treating a target region in tissue beneath the tissue surface comprise a probe having a distal end adapted to be positioned beneath the tissue surface and within or just proximal to a target region in the tissue. A plurality of electrodes are deployable from the distal end of the probe to span a region of tissue proximate the target region, usually just distal to the site. The system further includes a cover, such as a surface electrode, adapted to span an area of the tissue surface over the target region. Other exemplary covers include rigid plates, typically in the form of a disc having a generally circular or oval periphery, conformable surfaces, such as foam layers, polymer discs, deployable electrode structures having tissue-contacting surfaces, or any other mechanical structures which can be deployed over or contacted against tissue to provide a relatively uniform compressive force against the tissue. Preferably, a surface electrode comprises a support having an electrode face and an insulated face opposite to the electrode face. In the first embodiment, the electrode face may be generally flat and have an area in the ranges set forth above. Alternatively, the surface electrode may comprise a plurality of tissue-penetrating elements on the face of a plate or other support structure, typically from four tissue-penetrating elements to sixteen tissue-penetrating elements, more preferably from six tissue-penetrating elements to nine tissue-penetrating elements. Optionally, the tissue-penetrating elements may be arranged in a circular, grid, concentric ring, serpentine, zig-zag, staggered, or other pattern on the electrode face, further optionally with additional electrodes interior to the peripheral electrodes. The tissue-penetrating elements preferably comprise pins having the sizes described above.
The surface electrode may optionally be connected to the probe using a connector. Usually, the connector will attach the surface electrode in a generally transverse orientation relative to the axis of the probe. Optionally, the connector can be flexible or in the form of a swivel or xe2x80x9cuniversal jointxe2x80x9d which permits the surface electrode to align itself with the tissue surface even when the probe is entering at an angle relative to the tissue surface which is not perpendicular. Other suitable connectors include clips, pinch clamps, threaded connectors, hook and loop fasteners (such as VELCRO(trademark) brand fasteners), and the like. The connectors should allow the surface electrode or other cover to be selectively attached at various points along the length of the probe. Optionally, the probe can be marked with indicia indicating the depth of penetration, i.e., length between the distal tip of the probe and the particular point on the probe where the surface electrode or other cover may be attached. The ability to connect the surface electrode or other cover to the probe prior to deployment of the first electrode array is useful in helping to position the probe at a desired treatment depth, as described elsewhere herein.
The surface electrode and the probe may be electrically isolated from each other or may be electrically coupled to a common pole for monopolar operation. For simultaneous monopolar operation, the surface electrode (and any tissue-penetrating elements thereon) will be electrically coupled to the deployable electrode array on the probe so that all of the electrodes in the system can be connected to one pole of an electrode surgical power supply. Alternatively, the array electrodes on the probe may be electrically isolated from the second electrode and any tissue-penetrating elements thereon. When electrically isolated, the electrode array and surface electrode can be driven separately (one at a time) in a monopolar fashion or simultaneously in a bipolar fashion, i.e. each connected to the opposite pole of an electrosurgical power supply.
The probe will usually comprise a cannula having a proximal end, a distal end, and a lumen extending to at least the distal end. The deployable electrodes are resilient and disposed within the cannula lumen to reciprocate between a proximally retracted position where all electrodes are radially constrained within the lumen and the distally extended where all electrodes deploy radially outwardly. Usually, the electrodes will have a shape memory which will deflect the electrodes radially outwardly as they extend from the cannula. The most preferred configuration for the deployable electrodes is arcuate so that they assume an outwardly everted configuration as they are extended from the cannula. Usually, the array electrodes are connected to a rod structure which is reciprocatably received in the cannula lumen. Optionally, a stylet may be provided as part of the system for placement in the cannula so that a sharpened tip of the cannula extends beyond the distal tip of the cannula. The cannula and stylet may then be introduced to the target region through tissue, after which the stylet is removed leaving the lumen for receiving the electrode array. Usually, the cannula will have a length in the range from 5 cm to 30 cm, preferably from 12 cm to 25 cm, and an outer diameter in the range from 1 mm to 5 mm, usually from 1.5 mm to 2 mm. The electrode array will deploy outwardly to a radius in the range from 0.5 cm to 3 cm, preferably from 1 cm to 2 cm when fully extended. The electrode array will include at least 5 electrodes, preferably including at least 8 electrodes and often including 10 or more electrodes.
Kits according to the present invention will comprise at least a second electrode, together with instructions for use for deploying an electrode array in tissue and engaging the second electrode on a tissue surface above the deployed electrode array for treating a tumor or other disease condition at or near the tissue surface. Usually, the second electrode (optionally together with a first electrode array) will be packaged in a conventional medical device package, such as a tray, box, tube, pouch, or the like. The instructions for use may be provided on a separate sheet of paper or may be printed in whole or in part on a portion of the packaging.